Critical milestones include comparison between vaccinated and vaccine-controlled children of 1) pneumonia incidence (vaccine efficacy against pneumonia), 2) influenza incidence (vaccine efficacy against influenza) 3) rates of other clinical syndromes (vaccine efficacy against other childhood morbidity). Milestones related to secondary objectives include comparison between vaccinated and vaccine-controlled children of 1) rates of laboratory-confirmed infection and clinical illness among household contacts and 2) rates of other invasive bacterial and viral diseases, and 3) rates of adverse events. We will also measure childhood immune responsiveness to influenza vaccine and relate that to observed rates of infection and clinical illness.